1. Field of the Invention
The invention relates to a housing configuration for a laser module with a hermetically sealed module housing. The module housing contains the laser module and has at least one transparent wall portion. A carrier plate either forms the base of the module housing or carries a housing base of the module housing. The housing configuration also includes a device for coupling a wave guide to the module housing.
A conventional housing for cooled laser modules, a so-called butterfly housing, includes a metallic baseplate, on which a cooling element, with a laser module provided on it, and possibly further optical elements are attached. The housing is closed in a hermetically sealed manner with a metal cover that is welded or soldered to the housing. The coupling-of the optical fiber takes place via a fiber flange attached to the housing in the region of a housing window. With such a housing, data rates of over 2.5 Gbit/s can be achieved. However, due to the requirement for a hermetic sealing, the housing as such, its electrical lead-throughs and the sealing of the optical window have to meet high requirements. Furthermore, only components and materials that release no gas or vapors can be used in the housing. For these reasons, optoelectronic components provided with such housings are relatively expensive.
U.S. Pat. No. 5,566,265 discloses a so-called TO (Transistor Outline) housing, which is used for the operation of uncooled laser modules. This housing can be produced at low cost. However, it is disadvantageous that this housing cannot be used for wavelength-stable laser modules, since the temperature cannot be stabilized, and that, due to the presence of RF lead-throughs on the baseplate side in the form of glazed-in pins, which hinder RF coupling at high frequencies, this housing is only partly suitable for data rates of over 2.5 Gbit/s.
It is accordingly an object of the invention to provide a housing configuration for a laser module which overcomes the above-mentioned disadvantages of the heretofore-known housing configurations of this general type and which can be produced at low cost, makes a high data rate possible and, in particular, is also suitable for wavelength-stable cooled laser modules.
With the foregoing and other objects in view there is provided, in accordance with the invention, a housing configuration for a laser module, including:
a hermetically sealed module housing configured for receiving a laser module;
the hermetically sealed module housing having at least one laser-light-transparent exit wall portion and having a carrier plate as a base;
the hermetically sealed module housing having a cap formed of a laser-light-transparent material selected from a laser-light-transparent glass or a laser-light-transparent silicon, the cap being integrally formed and coupled to the carrier plate in a hermetically sealed manner;
the carrier plate including an RF conductor track carrier formed of a dielectric material;
an RF conductor track section guided along the RF conductor track carrier for providing an electrical RF contact to the lager module; and
a coupling device connected to the hermetically sealed module housing and to be connected to an optical wave guide.
With the objects of the invention in view there is also provided, a housing configuration for a laser module, including:
a hermetically sealed module housing configured for receiving a laser module;
the hermetically sealed module housing having at least one laser-light-transparent exit wall portion and having a carrier plate as a base;
the hermetically sealed module housing having a circumferential wall formed of a laser-light-transparent pipe section;
a top plate terminating the pipe section, the top plate being a ceramic plate or a metal plate;
the carrier plate including an RF conductor track carrier formed of a dielectric material;
an RF conductor track section guided along the RF conductor track carrier for providing an electrical RF contact to the laser module; and
a coupling device connected to the hermetically sealed module housing and to be connected to an optical wave guide.
With the objects of the invention in view there is further provided, a housing configuration for a laser module, including:
a hermetically sealed module housing configured for receiving a laser module;
the hermetically sealed module housing having at least one laser-light-transparent exit wall portion and having a carrier plate as a base;
the hermetically sealed module housing having a circumferential wall formed of a pipe section, the pipe section being a ceramic pipe section or a metal pipe section;
a laser-light-transparent top plate terminating the pipe section;
the carrier plate including an RF conductor track carrier formed of a dielectric material;
an RF conductor track section guided along the RF conductor track carrier for providing an electrical RF contact to the laser module; and
a coupling device connected to the hermetically sealed module housing and to be connected to an optical wave guide.
With the objects of the invention in view there is additionally provided, a housing configuration for a laser module, including:
a hermetically sealed module housing configured for receiving a laser module;
the hermetically sealed module housing having at least one laser-light-transparent exit wall portion and having a carrier plate;
the hermetically sealed module housing having a housing base, that is different from the carrier plate, and having a circumferential wall;
the circumferential wall being cap-shaped in accordance with a TO housing cap and having a cover side;
the carrier plate including a body of a material with a good thermal conductivity and including an RF conductor track carrier formed of a dielectric material provided on the body on a side thereof facing the housing base;
a laser-light-transparent window being attached in a hermetically sealed manner at the cover side;
an RF conductor track section guided along the RF conductor track carrier for providing an electrical RF contact to the laser module;
the housing base being formed with a contacting bore;
a contacting pin extending in an electrically isolated manner through the contacting bore and being electrically contacted with the RF conductor track section; and
a coupling device connected to the hermetically sealed module housing and to be connected to an optical wave guide.
To achieve the object of the invention, the carrier plate includes an RF conductor track carrier formed of a dielectric material, and an RF conductor track section is guided on the RF conductor track carrier for an electrical RF contacting of the laser module.
The RF conductor track section running on or in the carrier plate achieves the effect that the module housing has the desired good RF properties. At the same time, it is ensured by the carrier platexe2x80x94in that it bears the housing base of the module housing or even itself forms the base of the module housingxe2x80x94that a good thermal coupling of the carrier plate to the laser module can always be achieved. This makes it possible for the laser module to be operated at a stable temperature and consequently for wavelength-stable laser modules to be provided, as are required for optical transmission systems with WDM (Wavelength Division Multiplexing) transmission.
A further major advantage of the invention is that a low-cost overall construction is made possible for several reasons. Firstly, the module housing as such can be produced in a very cost-saving way. If the carrier plate forms the base of the housing, the latter can be made up in a simple way of a cap placed onto the carrier plate in a hermetically sealed manner. In the other case (i.e. if the carrier plate bears the housing base), already existing, low-cost TO housings can be used for constructing the housing configuration according to the invention after shortening their lead-through pins and mounting them on the carrier plate according to the invention in the manner of an SMD (Surface Mounted Device). As a result, the known benefits of circuit configurations produced by the SMD technique are achieved. All further optical elements possibly provided, which are disposed outside the module housing, do not have to meet the requirements of a hermetically sealed construction, i.e. low-cost configurations which may contain epoxy resin can be chosen for them. The invention consequently provides a module housing which is functionally independent, can be configured in a constructionally compact way and is hermetically sealed, which forms a xe2x80x9ccore unitxe2x80x9d for the housing configuration according to the invention and, as a result, makes a high degree of modularity or configuration variability possible for the construction of the housing configuration according to the invention.
For example, the coupling of a light guide or wave guide can take place completely separately from the module housing either on a xe2x80x9crelocatedxe2x80x9d optical component or an outer housing.
Already completely produced and tested coupling devices can be used for the coupling, whereby yield problems in final assembly can be significantly reduced.
The RF conductor track section is preferably configured as a coplanar line or microstrip line and has a characteristic impedance in the range of 25 xcexa9 to 50 xcexa9.
According to a preferred configuration of the invention, the carrier plate forming the base of the module housing is made up just by the RF conductor track carrier formed of the dielectric material. Apart from the RF conductor track section, contact pads, further conductor tracks and possibly also further components such as thin-film resistors, integrated hybrid amplifiers etc. may also be provided on such a carrier plate. A carrier plate formed of a material with good heat conduction, such as Al203, BeO or AlN, is preferred, because such a carrier plate has good thermal conductivity for carrying away lost heat of the laser module.
An alternative, likewise preferred configuration of the invention is characterized in that the carrier plate forming the base of the module housing is made up of the RF conductor track carrier and a metal layer provided over the RF conductor track carrier and formed in particular of Cu, a Cu/W alloy or xe2x80x9cKOVAR.xe2x80x9d In this case, the lost heat produced by the laser module is distributed and carried away in an efficient way via the metal layer provided on the surface side. In the case of a cooling, the metal layer improves the thermal coupling of the laser module to a cooling element.
Furthermore, the RF conductor track carrier may also be configured as a multilayer printed circuit board. In this case, crossovers of conductor tracks running in different layers are made possible, and, in the presence of a sealing ring provided on the surface, the conductor tracks can be led through under the ring without any problem.
If, as already mentioned, a TO housing with its own housing base is used as the module housing, a preferred variant of the invention is characterized in that the carrier plate is made up of the RF conductor track carrier and a body of a material with good thermal conductivity, in particular metal, the RF conductor track carrier being provided above the body. Since the RF conductor track carrier in this case does not contribute to the heat dissipation, but tends to hinder it instead, it can preferably be very thin, for example configured as a foil.
A first exemplary embodiment of the housing configuration according to the invention is characterized in that an optical element is provided behind or downstream of the module housing as seen in the direction of the path of rays of the laser light beam, and in that the optical light guide or wave guide can be fixed in a mechanically stable position on the optical element. In the case of this exemplary embodiment, the already mentioned possibility created by the invention of relocating optical elements out of the hermetically sealed module housing is utilized by the coupling of the optical wave guide taking place directly on this relocated optical element.
The relocated optical element may be, for example, a deviating prism or an optical isolator.
An advantageous configuration of this solution is characterized in that the housing configuration is surrounded by a protective sheathing brought about by a foaming process and/or encapsulated with a plastic with poor heat conduction. As a result, environmental influences can be kept away from the module housing. If a cooling element, for example a Peltier cooling device, is provided, thermal isolation of the same is also achieved in an advantageous way.
The housing configuration may also be surrounded by a protective housing of plastic. This protective housing may be a simple plastic housing, the task of which is to protect the housing configuration, and in particular the relocated optical element, from dust and to prevent heat exchange by convection.
A second preferred exemplary embodiment of the invention is characterized in that an outer housing is provided behind (i.e. downstream) the module housing as seen in a direction of the path of rays of the laser light beam and in that the optical wave guide can be fixed in a mechanically stable position on the outer housing. Since the outer housing does not have to be hermetically sealed, it may be made up of lowcost materials, such as for example plastic and metal, making it possible to dispense with expensive hermetically sealed line lead-throughs and hermetically sealed windows. For the optical components provided in the outer housing, outside the hermetically sealed module housing, low-cost configurations containing plastic or epoxy resin can also be chosen.
According to an expedient configuration, the cap of the module housing may be integrally configured and be formed of a laserlight-transmitting material, for example glass or, in the case of adequately longwave laser radiation, also silicon. It is also possible, however, to construct the cap from a piece of pipe forming the circumferential walls and a top plate closing off the piece of pipe at the end. In the case of a laser module whose path of rays runs parallel to the carrier plate, the piece of pipe may be formed of a laser-light-transmitting material, for example glass or silicon. By contrast, in the case of a laser module radiating perpendicularly with respect to the carrier plate, the laser light must be able to pass through the top plate. This then is preferably formed of glass or silicon, while the piece of pipe forming the circumferential walls of the module housing may be formed from ceramic or metal.
The carrier plate is preferably coupled to a cooling element, in particular a Peltier element, provided outside the module housing, whereby wavelength-stable modules are achieved.
According to another feature of the invention, the module housing includes the carrier plate and a cap coupled in a hermetically sealed manner to the carrier plate.
According to yet another feature of the invention, the cap is of an integral configuration and is formed of a laser-light-transmitting material, in particular glass or silicon.
According to a further feature of the invention, the cap is made up of a piece of pipe forming the circumferential walls and a laser-light-transmitting top plate, the piece of pipe is formed in particular of ceramic or metal and the top plate is formed in particular of glass or silicon.
According to another feature of the invention, the cap is made up of a laser-light-transmitting piece of pipe forming the circumferential walls and a top plate, the piece of pipe is formed in particular of glass or silicon and the top plate is formed in particular of ceramic or metal.
According to yet another feature of the invention, the module housing is made up of a TO cap with a housing base provided on the carrier plate side.
According to another feature of the invention, the housing base of the module housing is provided with a contacting bore, through which a contacting pin is led in an electrically isolated manner and is in electrical contact with the RF conductor track section, a portion of the contacting pin running between the housing base and the RF conductor track section having as small a length as possible, in particular less than 1 mm.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a housing configuration for a laser module, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.